Thermionic circuits and method



Oct. 21, 1941. E. R. JAHNS THERMIONIC CIRCUITS AND METHOD Filed March16, 1939 2 Sheets-Sheet 1 INPUT INVENTOR Edward RJa/ms )2 M 677A,"ATTSRNEYS Oct. 21, 1941. JAHNS 2,259,471

THERMIONIC CIRCUITS AND METHOD Filed March 16, 1959 2 Sheets-Sheet 25WITCH INPUT INVENTOR Egz uard RJa/"ms 3%] f M ATTORNEYS Patented Oct.21, 1941 I U 1 TED TAT-Es Pierm so FFI CE 7 V TI' IERMIGNIG AND METIIODv corporation of Delaware Application Marchlfi, 1939, Serial N0. 262,123Claims. (01. 25027) The present invention relates to circuits of thetype usedin radio receivers, amplifiers or the like and comprises a newmethod of providing heater power for indirectly heated cathode tubeswhich improves the operation of the tubes and which utilizes oneelement-to perform: the functions which heretofore required theprovision of two or more separate elements. The invention includes alsonew circuit arrangements suitable for carrying out the new method.

object of the invention is to provide a method of and means forsuppressing the hum in tubes employingother than pure D. as a source ofpower for indirectly heated cathodes.

A'further object of the invention is to improve the operation or radioreceiver's, amplifiers or the like employing alternating current or anysource of supply other than pure direct current.

These and other objects o'f the invention will become apparent as thedescription proceeds.

For an understanding of the invention reference may be had to theaccompanying drawings, of which:

Fig. 1 is a diagram illustrating generally the principle of theinvention;

Fig. 2 is a circuit diagram illustrating one embodiment of the inventionas applied to a simple A. C. operated amplifier; and

Figs. 3 and 4 are circuit diagrams illustrating modified forms of theinvention as applied to radio receiving circuits.

The general theory of the invention may be readily understood byreference to Fig. 1 in which four tubes, I, 2, 3 and 4, having cathodes6 and heater elements I, 8, 9 and III are diagrammatically illustrated.The particular number of tubes is of course immaterial. The circuit mayinclude a greater or less number of tubes. Tubes I, 2, 3 and 4 may beany four tubes of an A. C. operated radio set or amplifier connected inany order.

In accordance with the invention, the A. C. "hum of tubes I and 4 iseliminated. by passing cathode current from one or more tubes of thecircuit through heaters I and I0. Heaters 8 and 9 of tubes 2 and 3operate as usual on A. C. voltage. The cathode current or currentspassing through heaters I and III give a bias voltage to the tube ortubes supplying the current and consequently two bias resistors can beeliminated from the circuit.

Specific circuits embodying the invention will now be described.

In Fig. 2 is shown a simple A. C. amplifier cirl2whichis grounded at oneend and connected at its other end to the cathode I3 of the power outputtube I4 to serve as a bias resistor for that tube. The heater I5 for thecathode I 3 of the output tube is supplied-asusual from the A. C. sourcethrough the transformer I I).

Theyrest'of the circuit-being of conventional type needs no particulardescription. I The rectifier I! for supplyingthe plate voltage to tubesI I and I4 may be of the type known as #80, tube I I may be of the typeknown in the trade as GK? and the power output tube I4 may be of thetype known as 6V6. A bleeder resistor I8 connected between the cathodeI3 and positive voltage connection I9 may be employed if desired but itis not essential.

In Fig. 3 a conventional rad-i0 receiving circuit havingan amplifier 20,detector 2 I, power output cuit in which the amplifier tube II has aheater 55 tube 22 and rectifier 23 is shown. The heater 24 for the-cathode 25 of detector 2| operates as the bias resistor for the grid 26of the power output tube 22." For this purpose the heater24has one endgrounded and its other end connected to the negative voltage connection21.

Another specific embodiment of the invention is shown in Fig. 4 whereinis illustrated a conventional type radio amplifier having theaudiofrequency amplifiers 28 and 29, push pull power output tubes 30 and3|, and rectifier 32. The heater 33 for the cathode 34 of amplifier 28together with the heater 35 for the cathode 36 are so connected as toserve as the bias resistors for the grids of tubes 29, 30 and 3I and toreceive current from the direct current portion of the circuit. For thispurpose one end of heater 33 is grounded, as is cathode 36 and cathodes31 and 38 of output tubes 30 and 3|; the other end of heater 33 beingconnected through resistances 39 and 40 with the control grid 4| ofamplifier 29 and through heater 35 with the low voltage line 42 of therectifier 32.

From the above description of specific embodiments of the invention, itwill be apparent that hum is eliminated in one or more tubes of acircuit by supplying the cathode heaters of such tube or tubes withcurrent from the direct current portion of the circuit and that separatebias resistors for other tubes ofthe circuit are thus eliminated. Inpractice it has been found that the use of cathode current as heaterpower is moreefiective in suppressing hum than is the use of so-calleddirect current from a commercial power source unless such current is notpulsating and is strictly constant. Furthermore, the employment of acathode heater in the norto stabilize the cathode currents by virtue ofthecathode current, grid bias characteristics of the biased tube.

As the usual cathode current of a tube is ordinarily somewhat less thanthat supplied to cathode heaters by the separate source of voltagecustomarily used, the tube in which the heater is supplied with currentfrom the direct current portion of the circuit should preferably beredesigned to allow for the lower cathode wattage as will be wellunderstood by those skilled in the art. i

The following is claimed: v

1. In an alternating current operated circuit including a plurality ofthermionic tubes, a cathode heater for one of said tubes and circuitconnections for supplying said heater with the anode-cathode current ofanother of saidtubes whereby said heater is heated by unidirectional 7current and said connections being such'as to enable said heater toserve as a bias resistor for said last-mentioned tube.

2. In an amplifier circuit or the like operating by alternating currentand including at least one amplifier tube and an output tube, thecombination comprising a cathode heater element for the amplifiertube,'a cathode and a grid for theoutput'tube and electrical connectionsbetween said amplifier heater and said output tube to cause thecurrentthrough the cathode'of said output tube to pass through said heater andthe resulting voltage drop across said heater to operate as a biasvoltage for the grid of said output tube.

3. In a radio receiving set operating by alternating current and havinga detector, a power output tube and a rectifier having high and lowvoltage conections leading therefrom, the combination comprising acathode heater for the detector and a cathode and grid for the outputtube, one end of said heater being grounded and the other end of saidheater being connected to the low voltage connection of said rectifierand to the grid of said output tube whereby said heater is supplied withunidirectional anode-cathode current from said tube and operates as abias resistor for the gridthereof.

7 4. In an amplifier circuit operating by rectified alternating currentand having at least one amplifier tube and an output tube, thecombination comprising a cathode heater for the amplifier and a cathodeand a grid for the output tube, said heater having one end grounded andhaving itsother end connected to said cathode of the output tube andsaid grid being connected to ground, whereby said heater serves as abias resistor for said output tube.

5; In an amplifying circuit or the like operating by alternating currentand having two amplifier tubes, two output tubes connected in pushpullrelation and a rectifier having high and low voltage connections leadingherefrom, the combination comprising a cathode heater for each amplifiertube, one end of one heater being grounded and one end of the otherheater being connected to said low voltage connection of said rectifierand the other ends of said heaters being connected together to a pointin the grid circuit of one of said amplifiers whereby said heaters aresupplied with unidirectional current from said output tubes and operateas bias resistances for the output tubes and for said last mentionedam-, plifier.

EDWARD R. JAI-INS.

